In a multi-node wireless network, such as a cellular radio network, each information stream is typically transmitted on its own radio resource, channel, so as not to result in interference between the different streams.
A multi-node wireless network generally uses a certain partition of the available spectrum for providing services. The available spectrum is divided into channels depending on the type of wireless network. Frequency-division multi-access (FDMA) uses different frequency bands for each channel. In time-division multi-access systems (TDMA), the channels are made up of time slices or time slots on a frequency band. The channels may also be defined through code-division multi-access (CDMA) or any combination of these techniques. In LTE/OFDM systems the scheduling resources is a physical resource block pair. Regardless of the system in use, the different channels should ensure isolation between different information streams. However, as the available number of channels is limited, the channels must be reused within different geographical sub-areas, so-called cells, in order to provide coverage and capacity. With an increasing number of wireless devices, there is an increasing need for further optimized use of the limited number of available channels in a wireless network.
Depending on technology choices and factors such as what multiple access techniques that are employed and how robust to interference the information stream receivers are, reuse of the radio resources, channels, may be possible within a cell. If it can be determined that paths of two separate streams are sufficiently isolated from each other, they could then potentially carry out their individual transmissions on identical channels and still not interfere with each other, resulting in a re-use of the valuable limited channel resource.
In the wireless network, information streams between communication nodes are set up on radio resources, also denoted as channels. The radio resource may be a frequency in a FDMA system, a time slot in a TDMA system, a resource block in a OFDM system or any other type of radio resource. Isolation between different information streams in the network is ensured by use of non-overlapping radio resources. Re-use of the same radio resource for transmission of different information streams between multiple sets of communication nodes, is possible only when the information streams are sufficiently isolated from one another. The cellular planning of a wireless network is based on the possibility to re-use channels that are sufficiently distanced from one another. However, information streams may be sufficiently isolated to allow for a more optimal channel or radio resource re-use.
The primary problem with re-using channels lies in the determination of whether independent streams are sufficiently isolated from each other. A conventional way to determine if two sending nodes can transmit on the same channel is done via measurements of the different signal powers at the receivers. Typically, the receivers would measure the received signal strength of their “own” source's transmission, as well as the signal strength of the “other” source's transmission, and potentially also the ‘ambient’ background signal strengths. By analyzing the combination of these various signal power levels, together with knowledge of the receiver's hardware characteristics, it can then be possible to estimate whether both transmitters can transmit simultaneously on the same channel, while each receiver only receives its intended information.
EP, 1589776 discloses a method and an arrangement for allocation of radio resources in mobile communications systems, wherein the mobile stations perform measurements of pilot signal power to enable increased channel reuse. The mobile station measures quality measures of signals transmitted from a multitude of base stations. The measurements are reported to a base station that assigns resources based on the measurement results. The disclosed method and arrangement improves the possibility for channel re-use in a wireless network, but is still based on determination of channel isolation from mobile measurements and reported signal strength values.
However, determinations on channel re-use based on signal power measurements from the terminals is not trivial to carry out and a conclusive outcome difficult to ascertain. Hardware imperfections would make it difficult for the control node to estimate with confidence what each receiver can successfully decode. Furthermore, the receivers may be different types of devices with different receiver sensitivities, e.g., mobile handsets as compared to low-power sensors, making it even more challenging for the control node to make an accurate estimation without specific knowledge of the types of receiver hardware involved.